I hope it's ok to post this here, as I'm using TomatoRAF but posting in the Linksys forum, as a new user, takes several days for posts to show.
Yesterday I installed TomatoRAF (tomato-K26USB-1.28.8703MIPSR1_RAF-VPN) on my Asus WL500gPv2 and configured my tunnel to HE. At first everything seemed to be working correctly, I was able to ping -6 various ipv6 sites, however, when I attempted to browse the HE forums, the browser just timed out. This was repeated on a number of other ipv6 enabled sites, although ipv6.google.com had no such problem.
After searching the Internet I found several references to others with similar problems, not all using a Tomato variant. The common denominator seemed to be MTU size. After checking the settings in the router (MTU = 0 = Defaullt) and in Windows 7 IPv6 MTU = 1500, I decided to follow some advice given at http://www.sixxs.net/faq/connectivity/?faq=mtu which suggests setting the MTU, in Windows, to 1280. I did this and everything worked as expected.
However, This is not the first time I've created a tunnel with HE, in fact I used to terminate the tunnel directly on the PC before I purchased a router, but I couldn't remember having to make changes to the MTU at that time, so I decided to try again.
In this exercise, I removed the router and connected directly to the Internet, with a fresh install of Windows 7 Ultimate and all security disabled. I configured the tunnel and applied the settings via netsh. I then went through the testing procedure again. This time everything worked immediately. I didn't have to change the MTU.
So, my question is, why do I have to change the MTU size in Windows when the tunnel is terminated on the router but not when the tunnel is terminated at the PC? Perhaps I've misunderstood, but I thought with IPv6 fragmentation only occurs at the source and not on the routers. I also thought PMTU was responsible for discovering the MTU.
As it turns out, it would seem the optimal MTU size on my PC is 1440. This I confirmed by using tracepath6 from a Suse installation I have and also by adjusting the buffer size with ping -6 -l from my Windows 7 box.
Thanks for any help :)